EMU Volume 15 – Chapter 4

Hypervelocity impacts are a fundamental and quite common process in the Solar System. Extreme pressures, temperatures and stress and strain rates characterize an impact event. These unique transient physical parameters result in unique geological and mineralogical phenomena that include the formation of (macroscopic) shatter cones, and shock effects at the scale of minerals. Adiabatic pressure release and post-shock heating generate decomposition, melting and vaporization of rocks. In this chapter these shock and post-shock effects are discussed in terms of formation processes and characteristic features. A case study on the Lake Bosumtwi crater illustrates geochemical aspects of impact melt formation. Key facts about the high-pressure mineral phases in strongly shocked meteorites are discussed. Finally, key results of a unique series of meso-scale cratering experiments (‘The MEMIN project’) provide details of the role of target porosity in cratering efficiency and the ejection process.